The concept of IN was brought forward by Bell Communication Inc. and American Technology Corporation in 1984 and standardized by Consultative Committee for International Telephone and Telegraphy (CCITT) in 1992. It is a system that is able to generate and implement various new services in a fast, convenient, flexible, inexpensive and effective way. The objective of the IN is to serve all types of communication networks, including existed fixed communication networks such as a Public Switched Telephone Network (PSTN) and an Integrated Services Digital Network (ISDN) as well as mobile communication networks such as a Global System for Mobile Communication (GSM), a Wideband Code Division Multiple Access (WCDMA) system, a north America Code Division Multiple Access (CDMA) system and a CDMA2000 system.
Along with the development of communication networks, users' requirements to services keep rising. The objective of the IN is to provide users with new services in a fast, convenient and inexpensive way. To achieve the objective, a characteristic in design of the IN is to separate service handling process from call handling process.
In a network without an IN, every supplementary service for users is implemented through adding corresponding software and hardware in every network node. Therefore, exchangers in the network need to be upgraded accordingly to add or to modify a service.
But in a network with an IN, exchanger acts as a Service Switching Function (SSF), which is just responsible for basic switching functions, while all the intelligent services are handled by another network layer, which is the intelligent network. The SSF in the TN is used for switching. It reports various events in a call to a Service Control Function (SCF) and can hang up the call, waiting for further instructions from the SCF. The SCF accomplishes a service logic control.
The system structure of an IN is illustrated in FIG. 1. It should be noted that in a fixed IN in the prior art, the protocol adopted in the interface between a Service Control Point (SCP) and a Service Switching Point (SSP), as well as in the interface between the SCP and an Intelligence Peripheral (IP) is IN Application Protocol (INAP), which is defined by International Telecommunication Union Telecommunication Standardization Sector (ITU-T).
In order to implement intelligent services in the GSM/WCDMA system, Customized Application for Mobile network Enhanced Logic (CAMEL) is introduced. To support CAMEL services, three entities named as gsmSCF, gsmSSF and gsmSRF are added into the GSM/WCDMA system besides the existing Home Location Register (HLR), Visitor Location Register (VLR), Mobile Switching Center (MSC) and Gateway Mobile Switching Centre (GMSC). The gsmSSF is used for receiving instructions from the gsmSCF and reporting information of call status to the gsmSCF; the gsmSCF is the core of the mobile IN, which is used for executing CAMEL service logic, controlling call switching and charging etc; the gsmSRF is used for providing dedicated resources for services such as playing announcement and collecting user information
The functional architecture of a circuit switched domain that supports CAMEL in a WCDMA network is illustrated in FIG. 2A. It should be noted that the CAMEL service is implemented through the collaboration of a CAMEL Application Part (CAP) and a Mobile Application Part (MAP). The CAP protocol is used for the interaction among the gsmSCF, the gsmSSF and the gsmSRF. The CAP protocol is defined based on the INAP, while the capability set it supported in CAMEL Phase 1 to Phase 3 is a subset of IN Capability Set 2 (IN CS2) with special parameters or messages for mobile communication. In CAMEL Phase 4, the definition of Call Party Handling (CPH) capability is introduced, and the call model is developed to be consistent with that of IN CS2. And as the mobile application part, the MAP protocol is still used for supporting mobility-related features for users.
The CDMA mobile communication system in north America adopts American National Standard Institute (ANSI) 41D protocol. Similarly, in order to support the IN services, a series of Wireless IN (WIN) protocols were defined by stages on the base of the signaling structure and signaling flow in the ANSI 41D protocol by the Telecommunications Industry Association/Electronics Industry Association (TIA/EIA) of ANSI according to the IN CS2. Where, IS771 protocol was put forward in WIN Phase I, it defines technical requirements for WIN and provides services including a Calling Name Presentation (CNAP), a Voice Controlled Services (VCS) and an Incoming Call Screening (ICS); IS826 protocol was put forward in WIN Phase II, it provides WIN capability for Pre-Paid Charging (PPC); and IS848 protocol which is related to WIN Phase II was put forward in WIN Phase III, it mainly defines the services including a Rejection of Undesired Annoying Calls (RUAC), a Premium Rate Charging (PRC), a Freephone Service (FPH) and an Advice Of Charging (AOC). All the above protocols are finally integrated into ANSI 41E Protocol, which makes the ANSI 41E Protocol be a core network protocol totally based on the IN.
Both the CDMA ANSI-41 wireless IN and the GSM/WCDMA CAMEL mobile IN are derived from the fixed IN, therefore their system architectures are basically identical to that of the fixed IN: the intelligent layer is separated from the switching layer; service control is accomplished by the intelligent layer; the network includes the SSP (named as the gsmSSF in CAMEL architecture), the SCP (named as the gsmSCF in CAMEL architecture), the IP (named as the gsmSRF in CAMEL architecture), a Service Management System (SMS), a Service Creation Environment (SCE), etc; the functions of their functional entities are identical or similar although the service logics created and executed may be different.
However, while in the GSM/WCDMA CAMEL mobile IN, the CAMEL services are implemented through the collaboration of the CAP and the MAP, and the gsmSCF, the gsmSSF and the gsmSRF interact with each other through the CAP protocol, in the CDMA ANSI-41 WIN, interactions between the SCP and the SSP and between the SCP and the IP are implemented through different protocols, i.e., the ANSI-41 WIN protocol is the supplement of the ANSI-41 MAP protocol. Besides, though the CDMA ANSI WIN and the GSM/WCDMA CAMEL mobile IN share similarities in call model, trigger mechanism, etc., they are more or less different.
On the other hand, the IMS which adopts the IP packet switched domain as the bearer channel for its control signaling and media transmission, and adopts Session Initiation Protocol (SIP) as call control signaling, is introduced as an objective network of the WCDMA mobile network for implementing packet switched voice and packet switched data services and for providing uniform multimedia services and applications. In the IMS network, IP Multimedia (IM) value-added services are provided for IMS subscribers through various Application Servers (ASs), including an SIP AS, an Open Service Access Service Capability Server (OSA SCS) and an IP Multimedia Service Switching Function (IM-SSF), where, the IM-SSF provides mapping between the SIP protocol in the IMS and the CAP protocol in the circuit switched domain, and the SSP triggering capability, which enables IMS domain subscribers, e.g., subscribers of VoIP service, to seamlessly inherit the intelligent services provided in the WCDMA circuit switched domain.
FIG. 3 is a schematic diagram illustrating the IM-SSF interfaces. The IM-SSF supports three interfaces: a CAP interface, an ISC interface and an Si interface, where, the CAP interface is used for the interaction between the IM-SSF and the CAMEL Service Environment including the gsmSCF enabling the service control of the gsmSCF, and the ISC interface is used for the interaction between the IM-SSF and a Serving-Call Session Control Function (S-CSCF) enabling the service control of IP multimedia sessions. Via these two interface, the gsmSCF can finally perform corresponding control according to inside intelligent service logic through the IM-SSF over the IP multimedia sessions which are transmitted through the S-CSCF; and the Si interface between the IM-SSF and a Home Subscriber Server (HSS) is based on the MAP, and is used for downloading and updating CAMEL subscription data from the HSS.
In general, the foregoing technology in the prior art enables the IMS subscribers to seamlessly inherit the intelligent services of the WCDMA circuit switched domain through the mapping between the IMS SIP and the CAP protocol in the circuit switched domain and the SSP triggering capability provided by the IM-SSF.